The present invention relates to a novel loudspeaker construction and method of assembly therefor.
Typically, loudspeakers include a conical diaphragm or cone, formed of paper or other material, which is caused to vibrate by movement of a voice coil located near the apex of the cone. The cone may taper inward from a circular, elliptical, or polygonal base in a variety of configurations. Generally, the voice coil is wound on a thin cylindrical tube which moves within an annular gap of a magnet and is rigidly fixed to the cone. Such conventional loudspeakers may utilize a magnet assembly comprising several elements which are precisely aligned to provide an annular gap having a high gap flux. For example, the magnet assembly may include a ceramic magnetizable field member in the form of an annular ring, front and rear pole plates, and a cylindrical pole piece spaced within the front pole plate and field member so as to form the annular gap. For convenience, the term "magnet" will be used to refer to the entire magnet assembly in this specification.
Several constructions and methods have been devised for maintaining alignment of the elements of the magnet and for securing them to the loudspeaker chassis. The elements of the magnet may be mounted within a metal pot which is staked to a steel basket comprising the loudspeaker chassis during assembly. Although such construction provides some assurance that the annular gap is maintained, the elaborate configuration of the metal pot is expensive and illsuited to modern flat magnets. Another construction utilizes staking to secure a front pole plate to a steel loudspeaker basket while a rear pole plate and a field ring are cemented to the front pole plate by adhesive. Such construction facilitates fixing of the elements of the magnet to maintain the annular gap but, generally, results in distortion and weakening of the gap flux. Further, even with the use of modern adhesives, the elements of the magnet must be held in position for up to five hours while the adhesive cures, adding significantly to the manufacturing cost.
It has been suggested that a front pole plate may be secured to a molded plastic basket by encapsulating the edges of the front pole plate within a portion of the plastic basket. The remaining elements of the magnet may then be fixed to the front pole plate by adhesives in the manner previously described. This use of a molded plastic basket in place of a steel basket will reduce leakage of flux from the magnetic field within the annular gap and will result in a more uniform and higher level of gap flux. However, such suggested construction does not eliminate the manufacturing process in which the elements of the magnet are held in position while an adhesive cures. Further, such suggested construction leaves the field ring of the magnet visible and vulnerable to chipping and other damage, as only the front pole plate is encapsulated by the plastic basket.
It is therefore an object of the present invention to provide an improved loudspeaker assembly in which the basket of the loudspeaker does not reduce the magnetic flux within the annular gap and in which the elements of the magnet are not visible and are protected from chipping and other damage.
It is another object of the present invention to provide an improved method for securing the elements of a magnet of a loudspeaker to the basket of the loudspeaker such that material cost, manufacturing cost, and time of assembly are reduced while maintaining acoustical performance.
In conventional loudspeaker construction, the ends of the voice coil wire are electrically connected to flexible leads, generally formed of braided copper, which extend radially outward along the inside of the cone and are led through the cone to terminals supported from the loudspeaker basket to which the flexible leads are soldered. This manner of assembly is time consuming and requires considerable care and skill. Also, the flexible leads may interfere with the movement of the cone and may generate spurious sounds. Further, the flexible leads are subject to fatigue failure, particularly if solder penetrates the flexible leads and stiffens a portion of the flexible leads, a problem known as "wicking up" of the lead wires. Due to the frequency and amplitude of the vibration of the voice coil and cone relative to the basket of the loudspeaker to which the flexible leads are connected, breakage of the flexible leads is a major cause of loudspeaker failure.
It has been suggested that the flexible leads connected to the voice coil wires could be replaced by conductive strips painted upon or woven into a nonconductive centering disc or spider. However, the use of conductive strips upon a nonconductive centering disc or spider of a loudspeaker has been largely unsuccessful, in part because the known technology results in unacceptable resistance of the conductive strips and inability of the conductive strips to withstand repeated flexure or vibration. Other unsolved problems have been the high manufacturing cost of forming the conductive strips and difficulties related to establishing electrical connections between the conductive strips, the voice coil wires, and the terminals supported from the loudspeaker basket.
It is therefore a further object of the present invention to provide an improved electrical connection between the voice coil wires and the basket terminals of a loudspeaker by means of conductive strips having low resistance and the ability to withstand repeated flexure and vibration without impairment.
It is a further object of the present invention to provide an improved method of connecting the voice coil wires of a loudspeaker to a conductive strip formed upon a nonconductive centering disc or spider, resulting in ease of manufacture, reduced manufacturing cost, and positive electrical continuity.
It is a further object of the present invention to provide an improved method of connecting the terminals supported from the basket of a loudspeaker to a conductive strip formed upon a centering disc or spider of a loudspeaker resulting in ease of assembly, reduced manufacturing cost, and positive electrical continuity.
Particularly in loudspeakers designed for low frequency sound reproduction, conventional speakers may include a flexible member along the perimeter of the cone to facilitate axial displacement of the cone relative to the basket of the loudspeaker. Typically, this flexible member comprises a surround molded of a rubber or synthetic material which may be a thin layer of foam. The surround is generally cemented along its internal perimeter to the cone and along its external perimeter to the basket of the loudspeaker. A pad ring is often cemented to the front of the basket of the loudspeaker to provide clearance for the surround and to facilitate mounting of supplementary loudspeakers. The cementing of the pad ring and the surround to the basket of the loudspeaker tends to avoid undesired resonances, but the operation is time consuming and expensive and requires considerable care and skill.
It is therefore a further object of the present invention to provide an improved method of mounting the surround and the pad ring of a loudspeaker upon the basket of a loudspeaker resulting in ease of assembly, reduced assembly time, and decreased manufacturing cost.
One or more smaller loudspeakers may be mounted within the cone of a larger loudspeaker. Typically, a bridge, formed as a metal stamping, is screwed to the front of the pad ring to provide a mounting for one or more smaller loudspeakers. In a three-way loudspeaker system, for example, a tweeter and midrange may be mounted upon a bridge which is mounted upon the woofer of a loudspeaker system. However, the assembly of such a loudspeaker system is generally difficult and tedious because of the large number of separate parts involved and the practice of threading the flexible electrical leads from the tweeter and midrange through the cone of the woofer to the terminals supported from the basket of the loudspeaker. Further, the interaction of the flexible leads with the cone of the woofer may generate spurious sounds, and the separate parts may produce undesired "ringing" and resonances.
It is therefore a further object of the present invention to provide an improved method of electrically connecting one or more loudspeakers mounted within the cone of a larger loudspeaker to the terminals supported from the basket of the larger loudspeaker.
It is a further object of the present invention to provide an improved method of assembling a loudspeaker system having at least one smaller loudspeaker mounted within a larger loudspeaker such that a series of subassemblies can be easily joined together and such that all necessary soldering of electrical connections is completed before final assembly.
It is still a further object of the present invention to provide an improved loudspeaker system having at least one smaller loudspeaker mounted within a larger loudspeaker such that the number of separate parts is substantially reduced and in which adhesive is substantially eliminated.